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Technical Appendix
46
Technical Appendix
Signal-to-noise distance
The following values must be known in order to calculate the carrier-to-
noise distance (C/N) for analogue transponders.
• background noise level (set parabola antenna so that no satellite
signal is received)
• max. receiving level
• bandwidth correction.
This gives the following formula:
C/N = receiving signal level - background noise level - bandwidth correction
Measured bandwidth of MSK 24 6 MHz
Bandwidth correction value = 10 log ——————————————–--------
RF bandwidth of receiving signal
Bandwidth correction value = 6.37 dB at 26 MHz bandwidth (Astra)
Bandwidth correction value = 7.78 dB at 36 MHz (Eutelsat, Intelsat, Kopernikus)
Example
Receiving signal level +75.5 dB with satellite signal
Background noise level -55.0 dB without satellite signal
Carrier-to-noise distance C/N +20.5 dB
Bandwidth correction - 6.4 dB for 26 MHz bandwidth
C/N of the receiving system +14.1 dB
Note
To calculate C/N exactly, it is essential that you take the RF bandwidth of
the receiving signal into account.
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